program Square;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  x1, x2, x3, y1, y2, y3, s : integer;

begin
  readln(x1, y1);
  readln(x2, y2);
  readln(x3, y3);

  s := abs((x1 - x3)*(y2-y3) - (x2-x3)*(y1-y3)) div 2;
  writeln(s);
  readln;
end.
